io8 INTRODUCTION 



The last species forms a transition to pollen flowers with two kinds of stamens, 

 possessifig a?ithers of different form and colour. Among these are various Mela- 

 stomaceae. In Heeria, for example, the shorter upper 'nutritive anthers' are 

 resplendent with a dazzling yellow colour, while the reproductive stamens and the 

 style are red, passing into violet, like the petals, with which they consequently do 

 not contrast. We also find that the longer lower stamens have a lever-arrangement 

 on the connective. During a visit from one of the larger bees (Bombus, Xylocopa) 

 this keeps the anthers away while the guest is touching the style, and it is only when 

 the insect is leaving that the pollen-mass is pressed against its body. The colour- 

 contrast serves not only to attract insects to the more conspicuous nutritive anthers, 

 but also at once to direct the intelligent visitor to the right place. Among the Comme- 

 linaceae, Tinnantia undata shows similar differentiation of the upper and lower stamens 

 to those seen in Heeria. The modification of floral parts has gone somewhat further 

 in Commelina coelestis. Similar division of labour and differentiation in colour are 

 shown by the small simple white flowers of Heteranthera reniformis, one of the Ponte- 

 deriaceae. These possess a long stamen with pale blue anther-lobes, and two short 

 stamens with brilliant yellow pollen. In species of MoUia (Tiliaceae) and Lager- 

 stroemia (Lythraceae), the long stamens are green, the short ones yellow. As 

 Ludwig remarks in this connexion, the protection of pollen by inconspicuous 

 coloration is also common elsewhere. In the nectar flowers of Lythrum Salicaria, 

 for instance, the upper anthers are greenish, as also in Echium vulgare, where only 

 a few of the more inteUigent insects (e. g. Osmia) carry off the pollen. In Echium, 

 however, as in other gynodimorphous plants, the anthers of the smaller female 

 flowers, which only produce degenerate pollen, once more assume either a yellow 

 or some other conspicuous colour, thus serving to attract insects (op. cit., p. 483). 



2. Flowers with exposed Nectar (E). 



The lowest stage of nectar flowers (Ne) includes those with completely exposed 

 nectar, which is readily visible, and accessible to all visitors. Without exception 

 they are very simple, open, and for the most part radially symmetrical (actino- 

 morphous) flowers, generally white, greenish-yellow, or yellow in colour. The 

 following are examples: 



White: Most Umbelliferae, Parnassia palustris. Ilex Aquifolium, Lloydia sero- 

 tina, species of Saxifraga, Sambucus Ebulus, species of Galium, and others. Spotted 

 with yellow : Saxifraga stellaris, aspera, bryoides. 



Greenish-Yellow : Species of Acer, Petroselinum sativum, Rhamnus cathartica, 

 Euonymus europaeus, Alchemilla vulgaris, Saxifraga muscoides, species of Euphorbia, 

 Veratrum album ; Bupleurum falcatum, stellatum, rotundifolium, and others; Foenicu- 

 lum vulgare, Listera ovata and cordata, Pastinaca sativa, Anethum graveolens. 



Yellow : Chrysosplenium alternifolium and oppositifolium, species of Euphorbia, 

 Saxifraga Segueri and stenopetala, Gentiana lutea, and others. Spotted with orange- 

 yellow : Saxifraga aizoides. 



Fink : Meum IMutellina, Pimpinella rubra, Gaya simplex. Somewhat brighter 

 red : Azalea procumbens. 



